﻿USES OF COMMERCIAL WOODS. 23 



Fuel value. — 80 per * - < * 1 1 1 thai of white oak (Sargent). 



Breaking strength (modulus of rupture).. -14,900 pounds per square inch, 

 or 119 per cent that of white oak (Sargent). 



Factor of stiffness (modulus of elasticity). — 1,841,000 pounds per square inch, 

 or 139 per cent that of white oak (Sargent). 



Light, strong, hard, tough, compact; medullary rays numerous, obscure, color 

 brown, tinged with red; the sapwood nearly while. 



Height, 50 to 70 feel ; diameter, 6 inches to 3 feet. 



RANGE AND SUPPLY. 



The range of paper birch includes the northern tier of States 

 almost from ocean to ocean, extending into New York, Pennsylvania, 

 Illinois, and Nebraska, and northward almost to the Arctic Ocean. 

 Few trees of this country have a more extensive range, but it is not 

 everywhere of commercial importance. The tree is short-lived, and 

 the trunk is often defective. At. best, it is not an ideal timber tree 

 and in sohie regions where its size is fairly satisfactory lumbermen 

 are inclined to pass it by because of decay. It .endures cold, but un- 

 favorable climatic and soil conditions stunt the tree. On Mount 

 Washington, in New Hampshire, at an elevation of 5,700 feet, paper 

 birch is a prostrate shrub. It assumes a similar form near the north- 

 ern limit of its range in British America; but in other parts of its 

 habitat much good timber is found. The best appears to be in New 

 England, where the annual cut exceeds 30,000,000 feet. In Maine it 

 is rated second in stand among the hardwoods, while farther west, in 

 Michigan, Wisconsin, and Minnesota, it is often mixed with soft- 

 woods, such as white and Norway pine, balsam, fir, spru.ee, northern 

 white cedar, and tamarack. Frequently, however, it grows in pure 

 or nearly pure stands. 



It is known as paper birch, canoe birch, white birch, silver birch, 

 and large white birch. It is not readily mistaken for any other tree 

 with which it associates, for the tendency of its bark to roll up in 

 bands around the trunk is a noticeable characteristic. Several birches 

 shed their old bark in strips, but in almost all cases each species has 

 some feature which distinguishes it from paper birch. 



It is one of the few American species with a hold on the forest 

 stronger than it had when America was discovered. Large tracts are 

 now covered with this birch where there was little of it a century 

 ago. It is remarkably successful as a fire tree, one that pushes in and 

 occupies vacant spaces left by large forest fires. Some tracts thus 

 taken possession of within a century, or half a century, cover hun- 

 dreds of square miles. This birch is a prolific seeder, and the light 

 seeds are carried far by wind. When they fall on bare mineral soil, 

 free from shade, they spring up and grow vigorously. Paper birch, 

 however, is short-lived, and when some of the weaker trees begin to 

 fall other broadleaf species get a foothold, and finally the birch is 



